Polychloroprene rubbers

ABSTRACT

AN ADDITIVE FOR INCORPORATION IN POLYCHLOROPRENE RUBBER WHICH COMPRISES A PHYSICAL MIXTURE OF MAGNESIUM OXIDE AND AN INERT DILUENT POWDER WHICH IS COMPATIBLE WITH POLYCHLOROPRENE RUBBER, THE MIXTURE CONTAINING 10 TO 850 PARTS BY WEIGHT OF DILUENT POWDER PER 100 PARTS BY WEIGHT OF MAGNESIUM OXIDE.

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POLYCHLOROPRENE RUBBEHS Filed Jan. l0, 1972 lO Sheets-Sheet B 'May 7, 1974 G. A. ROHAN 3,809,567

POLYCHLQROPRENE RUBBERS Filed Jan. lO. 1972 A lO Sheets-Sheet 9 May 7, 1974 Filed Jan. lO, 1972 G. A. ROHAN 3,809,567

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United States Patent() 3,809,567 POLYCHLOROPRENE RUBBERS George Alexander Rohan, Esher, England, assignor to Kappa Holding A.G., Zug, Switzerland Filed Jan. 10, 1972, Ser. No. 216,441 Claims priority, application Great Britain, Jan. 12, 1971, 1,521/ 71 Int. Cl. C09c 1/02 U.S. Cl. 106-306 4 Claims ABSTRACT F THE DISCLOSURE An additive for incorporation in polychloroprene rubber which comprises a physical mixture of magnesium oxide and an inert diluent powder which is compatible with polychloroprene rubber, the mixture containing to 850 parts by weight of diluent powder per 100 parts by weight of magnesium oxide.

Itis known to use magnesium oxide in the processing of polychloroprene rubber for the purpose of preventing the setting up or prevulcanization of the mix as the result of the elevated temperature conditions prevealing during compounding of the rubber. In the unvulcanized compound magnesium oxide acts as a stabilizer preventing Stiffening and hardening up of the stock during storage and preliminary treatment of the rubber, e.g. extrusion or moulding, and later, under vulcanizing conditions, it acts in the presence of other metallic oxides as a crosslinking or vulcanizing agent and improves the ageing properties of the finished product.

The magnesium oxide used is generally specially manufactured for the purpose and isan extremely ne powder having a particle size range of up to 50 microns and preferably below 10 microns. Most commonly available grades of magnesium oxide have an average particle size of l15 microns but a special grade of magnesium oxide has a much smaller particle size in the range of 0.001 to 0.25 micron. The magnesium oxide is usually compounded in the rubber in powder form but this has several serious draw-backs in practice.

(1) The powder is highly hygroscopic and reacts with moisture in the air losing activity in the container if left open during storage.

(2) The extremely ne powder, which should be so far as possible entirely free from water when incorporated in the rubber, causes a number of diiculties in handling. It flies about in the air, contaminating instruments and equipment and it is a nuisance to the workers themselves.

(3) The powder is usually rather diflicult to compound into the rubber and its dispersion is seldom really perfect.

lf it is sought to overcome these difficulties by mixing the magnesium oxide with a liquid binder, which normally contains a mineral oil as its main constituent, to a pasty or putty-like consistency, the product sometimes tends to harden and lose its activity as the result of reaction between the oil and the powder. Also the equipment required to make this material and extrude it into a rod shape is expensive and tends to wear out quickly.

The invention provides an additive for incorporation in polychloroprene rubber which comprises a physical mixture of magnesium oxide and an inert diluent powder which is compatible with polychloroprene rubber, the mixture containing 10 to 850 parts by weight of diluent powder per 100 parts by weight of magnesium oxide. Owing to the extreme iineness of the magnesium oxide powder, the diluent powder is almost invariably coarser than the magnesium oxide powder. Indeed the diluent powder preferably has a particle size in the range of 1 to 200 times the particle size of the magnesium oxide po'wder.

3,809,567, Patented May 7, 1974 Fice Admixture with the magnesium oxide of the coarser diluent powder considerably reduces the tendency of the magnesium oxide powder to absorb atmospheric moisture and also to fly about in the air. Furthermore, the presence of the diluent powder facilitates uniform dispersion of the particles of magnesium oxide in the rubber partly by extending the magnesium oxide and so presenting it to the rubber in greater volume and partly by increasing the shearing stress in the matrix which is necessary for grinding-in and dispersion of the magnesium oxide powder in the rubber.

Preferably the additive contains, in addition to the powders, a liquid non-aqueous binder which may be found in an amount of 1-50% of the weight of the additive. Such binder improves the handling qualities of the additive and also facilitates dispersion of the magnesium oxide in the rubber. If incorporated in an amount of up to 10-50% by weight of the additive it yields a product in which the powder particles are agglomerated to form pellets.

Such pellets, as experiment has shown, absorb only 1% by weight of atmospheric moisture Whereas magnesium oxide powder absorbs 20% of moisture under the same conditions.

Preferably, however, the additive is made up in the form of tablets, which will normally contain 1040% by weight of binder.

The inert diluent powder can be chosen from the more or less inert mineral products that are usually used in such rubber mixes, for example, diatomite, china clay, calcium carbonate, barytes and talcum. Examples of other suitable diluent powders are: ball clay, fullers earth, dolomite, kieselguhr, lead oxide, finely pulverized siliceous minerals, limestone, magnesium carbonate, and certain powdered synthetic resins, for example polyethylene, phenol formaldehydre, urea formaldehyde and polyvinyl chloride. Two or more different diluent powders may be included in the additive.

Examples of suitable liquid binders are: Mineral oils, soya bean oil, rape seed oil, lecithin, maize oil, palm oil, hydrogenated rosin, butyl oleate, ethylene glycol, polyethylene glycol and its esters, polybutene, esters of phthalic acid and esters of phosphoric acid. In the case of mineral oil it may contain dissolved pitch, rosin or rosin derivatives. Two or more different binders may be included in the additive.

The additive may also contain other ingredients required in the polychloroprene rubber, for example, a plasticizer such as the reaction product of sulphuric acid with an unsaturated parafn or with a hydrophilic alcohol of high boiling point, or an anti-oxidant, such as a mixture of monoand diheptyl diphenylamine, tertiary butyl methylphenol, diphenylamine, di-isobutylene reaction product or alkyl aryl phosphates. Plasticizers are normally incorporated in polychloroprene in an amount of up to 10 parts by weight, anti-oxidants in an amount of up to 2 parts by weight and magnesium oxide in an amount of 3 to 4 parts by weight per 100 parts of chloroprene.

Accordingly, these additions can be incorporated in proportions of up to equal weight and more on the weight of magnesium oxide in the tablets. A corresponding amount, i.e., 3 to 4 parts by weight, of the mixed powder may be used.

Tests with the tabletted powders according to the present invention have shown that smaller quantities of magnesium oxide in the diluted blend have an equivalent effect to larger quantities of magnesium oxide powder alone due to the improved dispersion of the magnesium oxide in the rubber compound and apparent synergistic effect. In one typical example, one hundred parts by weight of ne Whiting powder were coated with 20 parts by weight of lecithin and 20 parts by weight of mineral naenesinm..nxide. powderandnabletted. Thesetablers when mixed into the rubber ycompound are equal in effect to the same total weight of pure magnesium oxide pow- `IIT-heinventiony.accordingly provides a process for the internal lubricationpf polychloroprene rubber which iny#cilinders .the step of. incorporating magnesiumA oxide into gtherubberasanadditive in any'ofr the forms described .above in,..particular, suchv a` process in which the .additive is incorporated into the rubber in van amount such :thatd-,the content 4of magnesium oxide in the rubber `rr'x]amounts only` to 0.5-.to 3% by weight, and preferably`1 to.29.z by weight.

The tablets according to the invention' may also cor1- tain additives to: assist. free yflow of the mixed powder ;;vghen the `tablets are disintegrated and also to assist in tabletting, for examp1e, ,-rnethyl cellulose, methyl-ethyl cellulose powder, starch oralginic acid. I

Whenfa's is preferred', calciumcarbonate is yused as ,the v,diluentpowder, itfmay bein the form-of whiting, ,softlnatural chalk, precipitated chalk or` a-crystalline Powdered mineral.

It is preferred s" `to vshape the tablets that they,will

nest ,to form a rod shape. Thus protrusions maybe formed :on one side of each `tablet and depressionson the other 'side these being sodisposed thatwhen thev tablets are packed 'the' protrusions and depressions on adjoining .tablets `willtit together to permit of nesting of the tablets. l'. [A preferred additive according tothe invention con- 'sists of a mixture of 75-15% by Weight of magnesium oxide and 25-85% by weight of diluent powder. The particle size of the magnesium oxide may be 0.001 to -50 microns and is preferably 0.001 to 0.2.5y micron. Such additive may consist of tablets containing 40% by weight of binder based on the weight of the powders, the amount of binder within this range being increased with lincrease in the content of magnesium oxide in the addi" tive.

The following are examples of typicaladditivesaccording to the invention: f

. 4 v Parts-by weight Magnesium oxide powder Vr vv50 China'clayvpowder 3.0 Lecithin 10 Oil' 10 lviagnesiinn oxide powder i'. -..Q -..l y 45 Dolomite powder: v l V40 -lroly'ethylene,glycol 200l rnonol-oleateA 5 v -Q- 10 y`(3) Magnesigm' nde powder '6s' Whiting ':-.f y v 20 Hydrogenated rosin l `5 2011 1-' .10

. 1 (4) y Magnesium oxide powder 'v r r so Whiting: `30 Butyl oleatc 5 031 f '1 15 Magnesium oxide powder 65 Whiting" 20 Hydrogenated ro'sn 5 i. (6) y i Magnesium oxide powder v'r i 35 Barytes Apowder 50 golyethylen'fglycol 400 dioleate c-; 15

(7) Magnesium oxide powder 20 Kieselghur powder 65 Polybutene 10 Polyethylene glycol 200 mono-oleate vnaphthenic oil, forl instance Gulf Rubber ProcessOiLof specific gravity 0.905 at 60 F., viscosity 204 seconds Redwood N051 at F. and aniline point 78.9 C. Au alternative oil which can be used, provided it 'is incorporated in the rubber in an amount not exceeding 2.5% by weight of oil, is Shellex 371, having a VVspecific; gravity of 0.9013 at 60 F., viscosity of 420 seconds' Redwood No. 1 and aniline point of 207 F. Y

All of the above 'formulations can be used without a binder in which case, for example, formulation 1 would consist of 62.5% by weight of vmagnesium oxide and `37.5% of china clay. .s v

The additivesy according to the invention should, be incorporated in the rubber in the drystate having` a moisture content not exceeding 0.50% `by weight. r

The following are examples of polychloroprene rubbers containing additives in accordance with theinvention:

" Parts by weight Neoprene GS 1'00 Magnesium "oxide mixed powder additive "'(Garo Y mag) 'l 4 Zinc oxide vf5 NA 22accelerator 0.5 HAF black 40 ,Stearic acid `0.5 Palal] WaX 1.5 Dutrex N (Shell softening oil) K H "3 PBN'(pheny1betanaphthylamine anti-oxidant) l v Parts by weight Neoprene GS y 100 Magnesium oxide mixed powder additive `(G3'0,'1G44' Y or G60) 1. 3 u .5 'f4 Zinc oxide v5 NA` 22 accelerator 01.25 SRF black 29 Parain wax v 1 Nonox DF (anti-oxidant) .I 1

Additives according tothe invention also have'the advanta-ge that they impart improved physical properties ,to the rubber as compared with magnesium oxide incorporated as vsuch in the rubber. This will be explained vwith reference tothe accompanying drawings, in,which:

FIGS. 1-5 are scorch curves comparing theyresults achieved with rubber in accordance withExample 8` above and a corresponding standard rubber formulation'4 to which.,the magnesium oxide was added as such andnot in admixture with a diluent powder, ,the curvesshowing the effect of variation in the content in the rubber of Garomag additive and of conventional magnesium oxide,

FIGS. 6 and 7 are curves showing the etfectof ageing` on these rubbers, and l f v if FIGS. 8-10 are curves comparingrubbers according v,to

- Example 9 and containing dierentadditivesaccording to the invention and a corresponding rubber to which .magnesium oxide was added as such and without admixture with a diluent powder. .4 f,

The comparison was made in the case.of (FIGS. 1.-7

- between rubber in accordance with Example .8 to which rubber to which had been 'added a corresponding amount of tabletted additive identified as Garomagflhis con;

sisted of a mixture of equal weights of Maglite D and powdered chalk to which had been added, prior to tabletting, a liquid binder consisting of 2 parts by weight of mineral oil and 1 part by Weight of lecithin, the binder constituting 15% by weight of the product.

FIGS. 1-5 show the Mooney plasticity, measured at 120 C., after varying times of exposure to that temperature, on a Mooney plastometer, of samples of polychloroprene to which had respectively been added Maglite D arid Garomag in amounts of 0.5%, 1%, 2%, 3% and 4% by weight of the rubber. As will be seen under the conditions of the test the rubber gradually becomes stier with increasing exposure to heat but this tendency is less pronounced with the samples containing Garomag, despite their smaller total content of magnesium oxide, than with those containing Maglite D. Moreover the disparity -between the curves in the various graphs increases with theduration of the test and also with the amount of additivi'v in the rubber, being most marked in the test with 4% of additive, i.e. with the conventional amount of magnesium oxide in the case of Maglite D. Since Garomag contains only a small amount of binder the improved softness of the rubber cannot be due to the mere presence of thebinder but may be due to a synergistic effect arising from improved presentation of the magnesium oxide to the rubber by the conjoint action of the binder and the diluent powder.

FIGS. 6 and 7 show the tensile strength and modulus at 300% (i.e. the force in pounds/sq. in. required to elongatea specimen by 300%) of specimens of polych1oroprene rubber containing various amounts of Maglite D and of Garomag expressed as parts per hundred, i.e. as percentages by weight of the rubber. The results shown in FIG. 6 were for unaged samples while those shown in FIG. 7 were for samples aged for 6 days at 70 C.

The curves in these ligures show that, while the samu ples containing Garomag had a slightly lower tensile strength in the unaged condition the modulus was considerably less. More significant is the fact that the change in tensile strength and modulus is considerably less in the samples containing Garomag. That this is so, will be seen from the following table which also shows the change in elongation at break on ageing.

FIGS. 8-10 show a comparison between rubber according to Example 9 to which 4 parts by weight of magnesium oxide has been added as Maglite D and rubber containing 4 parts by weight of tabletted materials identied as G30, G44 and G60. These were of the following formulation in parts by weight.

Magnesium oxide Ma lite D 60 vrom Label (Whiting 8 Binder 32 The binder in each case consisted of a mixture in equal parts by weight of Gulf Oil and lecithin. These curves show the superior performance of the materials G30, G44 and G60 notwithstanding the fact that the total content of magnesium oxide in the rubber was in each case substantially less than in the case of the rubber to which Maglite D alone had been added.

The Mooney plasticity curves at 120 C. for unaged stock shown in FIG. 8 demonstrate that the material containing Maglite D alone had a substantially higher Mooney plasticity than the other rubbers.

Maglite D produces a stiffer stock and the tablets produce a softer stock, the dierence being substantially greater than could have been achieved by the physical softening effect of the binder present in the tablets. It is |believed that the improved result may be due to a synergistic peptizing eect. FIGS. 9 and l0 show the effects of ageing of the rubber at 122 F. for 2 days and 6 days respectively. It will be noted that ageing has the effect of displacing all the curves vertically, the displacement being greater for the samples containing Maglite D than for those containing the tablets. Particularly signicant is the fact that the curve in FIG. 10 for Maglite D is entering the pre-cure or scorch area on the Mooney scale) after a period of six minutes, whereas the materials to which the tablets had been added remain in the unscorched area.

After curing for 17 minutes at 150 C. the materials to which FIGS. 8-10 refer had the following physical properties:

Tensile Percentage As will be seen the stocks obtained with the addition of the tabletted material have only slightly lower moduli than the stock containing Maglite D but have an equal tensile strength, which is the generally accepted criterion for the physical properties of polychloroprene rubbers.

The curves shown in FIGS. 8-10 show that there is very little diierence between the eiects obtained Iwith G30, G44 and G60, notwithstanding the substantial variation in the content of magnesium oxide in these additives.

A general similar improvement has been observed upon comparison of rubbers to which had been added Maglite D alone and Maglite D in admixture with Whiting lbut with insufficient binder to form tablets. 'I'he improved effect of the additives according to the invention has also been noted when magnesium oxide powder of coarser particle size of the order of 45 microns was used.

What I claim as my invention and desire to secure by Letters Patent is:

1. An additive for incorporation in polychloroprene rubber which comprises a physical mixture of 75-15 percent by weight of magnesium oxide and 25-85 percent by weight of an inert diluent powder which is selected from the group consisting of diatomite, china clay, calcium carbonate, barytes, talcum, ball clay, fullers earth, dolomite, kieselguhr, lead oxide, and magnesium carbonate, said magnesium oxide having a particle size in the range of 0.0010.25 microns and said diluent powder having a particle size coarser than that of the magnesium oxide.

2. An additive as claimed in claim 1, in which the diluent powder has a particle size in the range of up to 200 times the particle size of the magnesium oxide. 

